3S-GD2C2BR2 - AN ISOMORPH WITH A NEW STACKING-SEQUENCE

Gd2C2Br2 has been first described in [1]. Here we describe the new stacking variant 3s-Gd2C2Br2 prepared by reaction of stoichiometric amounts of GdBr3, Gd, and C at 1 320 K. 3s-Gd2C2Br2 with a stacking sequence different to that described in [1] crystallizes in space group C2/m with the lattice constants a = 706.6(2) pm, b = 382.7(1) pm, c = 996.7(4) pm and beta = 99.95(3)-degrees. In the structure C2 units are octahedrally surrounded by Gd atoms. Such Gd6(C2) octahedra are condensed via edges to form sheets, which are separated by two layers of Br-ions. In contrast to the modification described previously three slabs BrGd(C2)GdBr are stacked in [103] direction until identity is reached. The isotypic 3s-Tb2C2Br2 has also been prepared at 1 370 K. It is characterized by the lattice constants a = 701.5(3) pm, b = 380.1(1) pm, c = 994.8(3) pm and beta = 100.05-degrees.